John Parkinson — Gahhro of Pegli, N. Italy. 293 



glaucophane gabbro for a rock "near Pegli." This he describes 

 as being distinctly stratified, and as being characterized by- 

 possessing glaucophane in phxce of typical hornblende. Besides 

 glauGophane the rock is said to contain plagioclase, commonly titanite 

 or pyrites, and rarely quartz. 



It is also wortliy of remark that more recently'- a description has 

 been published by Chelussi ' of two glaucophane-bearing rocks from 

 the island of Giglio, situated to the west of the Orbetello peninsula 

 and not far south of the island of Elba. One of these is a gabbro in 

 which a diallage alteration takes place, resulting in the formation 

 of glaucophane, the dominant characteristic of the Pegli rock. The 

 other he calls a diorite, and compares with the rock Professor Bonney 

 and Professor Stefani have already noticed. He thinks that from the 

 sraallness of the constituents the rock might almost be called 

 a microdiorite, but that it approaches an amphibolite in its rather 

 schistose structure and in the abundance of its hornblende. The 

 glaucophane is present either as flakes, as iregular tabular crystals, or 

 as needles and fibres. The fact that these rocks present many points 

 of resemblance to the one near Genoa is, I think, of interest. Both 

 rocks are decomposed, that from Pegli the more so especially as 

 regards the felspars, but the likeness is sufficiently striking. 



M. Lacroix, in his work " Mineralogie de la France et de ses 

 Colonies " (vol. i, p. 706), describes many instances in which 

 secondary glaucophane results from the change — often a very 

 complete one — effected in various gabbros. Speaking of those rooks 

 from Viilarodin, near Modane, he remarks that the production of 

 glaucophane has been brought about by the usual methods of 

 uralitization, and that it may also be found in the midst of an 

 aggregate of epidote, albite, and calcite, which has resulted from the 

 saussuritization of the felspars. The occurrence of diallage as the 

 parent of glaucophane is apparently by no means uncommon, and 

 has been recorded several times in addition to the instances which 

 have been already mentioned. Professor Bonney, speaking of 

 glaucophane crystals from the neighbourhood of Zermatt,* remarks 

 that " their structure suggests to me the possibility of the replace- 

 ment of a diallage"; Mr. Eutley,^ in describing some glaucophane 

 epidote schists from M. Viso, remarks that the rock contains a little 

 diallage " sometimes enclosing numerous crystals of glaucophane " ; 

 and Professor Koto,^ writing on glaucophane from Japan, describes 

 many rocks in which this mineral is secondarily developed from — as 

 he believes — diallage ; one of these he compares with the Pegli rock 

 as regards the character of its groundmass. This author thinks the 

 very finely fibrous glaucophane often present in these rocks is 

 crocidolite, but owing to the nature of the mineral is unable to apply 

 a decisive test. In describing the rock from the Val Chisone * 



1 Atti E. Ace. Liucei, ser. v, Reiidic. iv (1895), p. 466. 

 "^ Mill. Mag., vol. vii, p. 7. 

 ^ Q,aart. Juum. Geol. tSoc, vol. xlv, p. 60. 



* Jouru. Coll. Sci. Imp. Univ. Toky5, vol. i (1886;, pt. 1 ; also Summary. Neues 

 Jahib. fur Miu. Geol., 1889, Bd. i, p. 36. 

 5 Miu. Mag., vol. vii, pp. 191-3. 



